1. Field of the Invention
The present invention relates to a television broadcast signal receiver for receiving digital television broadcast signals such as ATSC (Advanced Television Systems Committee).
2. Description of the Related Art
In the North American Continent such as the United States of America where ATSC digital television (hereafter referred to simply as “TV broadcast”) is broadcast, big cities spread across the plains. From the viewpoint of a television user or viewer to receive TV broadcast signals, which are broadcast in big cities or their suburbs, the TV broadcast signals or even one TV broadcast signal may come from various directions. Thus, it is necessary for the television user to adjust the direction of an antenna in the direction of a broadcast tower transmitting a television broadcast signal of a television program which the user wishes to watch.
For this reason, multi-directional antennas such as a so-called smart antenna are put to practical use. On the other hand, general antennas for receiving terrestrial broadcast signals have a shape of the so-called Yagi antenna, which has a high directivity to be able to receive a weak radio wave or signal. At the same time, the Yagi antenna has a drawback that it can receive only a radio wave from one broadcast tower due to the high directivity, hence the Yagi-antenna being a unidirectional antenna. Thus, currently, the multi-directional smart antennas and the unidirectional Yagi-antennas coexist.
Meanwhile, several methods are known for discriminating or determining the kind of an antenna to determine a receiving direction of the antenna. For example, Japanese Laid-open Patent Publication 2000-138928 discloses a method for discriminating between a community antenna type and a direct connection type such as a CS (Communication Satellite) antenna, using data of the respective broadcast frequencies. Further, Japanese Laid-open Patent Publication 2002-122651 discloses a method for discriminating between an active antenna and a passive antenna according to the presence or absence of an amplifier.
As described above, according to the ATSC digital television broadcast in the United States of America, the broadcast signals or waves may come from various directions, so that multi-directional antennas such as a smart antenna are needed to receive such TV broadcasts. The EIA (Electronic Industries Association)-909 standard provides a smart antenna having sixteen equiangular receiving directions in 360 degrees. A digital TV (television) broadcast signal receiver conforming to the ETA-909, standard is set to be able to adjust or switch an active signal receiving direction of the multi-directional antenna such as the smart antenna to every one of the sixteen receiving directions.
Some of such digital TV broadcast signal receivers have an omni-directional scan function (automatic scan function) to select the receiving direction of an antenna in which a digital TV broadcast signal of a channel selected by a TV user can be best received. This can be done by scanning the sixteen directions for each channel, and by setting the best receiving direction as a receiving direction for the channel, because usually the position of a broadcast antenna or a broadcast tower of a broadcast station does not change. However, in countries like the United States of America, broadcast stations may go into bankruptcy while it is relatively easy to open new broadcast stations. Accordingly, channels which could not previously be received may become receivable, while channels which could previously be received may become unreceivable. Furthermore, the receiving conditions of digital TV broadcast signals may change due to newly built high rise buildings. For this reason, it may be necessary to reset the best receiving direction for the channel selected by the TV user. In such case, a multi-directional antenna which can switch the receiving direction in a short time can be connected to a digital TV broadcast signal receiver having the omni-directional scan function.
When a user attempts to reset the best receiving direction, it may occur that the antenna then connected to the digital TV broadcast signal receiver is a general stationary unidirectional antenna, not a multi-directional antenna. If the user operates the digital TV broadcast signal receiver to attempt an omni-directional scan operation of the antenna without being aware that a multi-directional antenna is not connected to or disconnected from the receiver, the receiver cannot receive a TV program of a channel which the user desires to view unless the stationary unidirectional antenna happens to be pointed in the receiving direction for receiving the channel. At the same time, the digital TV broadcast signal receiver attempts, in vain, to omni-directionally scan all the sixteen directions, thereby causing a waste of time and energy for determining the best receiving direction. In a digital TV broadcast signal receiver, it is primarily important whether or not a multi-directional antenna is connected to the receiver.